To manufacture a steel for a low-temperature, high-pressure container having a high tensile strength (generally, of approximately 1100 MPa), a method of manufacturing a cylinder for a pressure container has been used in the prior art, which include: subjecting a seamless pipe to a spinning-type process. However, the cylinder prepared by the spinning-type process has problems in that the cylinder has a bad appearance due to the presence of seams in the cylinder, and its physical properties in the seamed portions may be deteriorated.
Also, since the steel is manufactured for purpose of the use in a seamless pipe, vanadium (V) used as a compound for carbide precipitation is often included in the steel after a quenching-tempering process. Therefore, when the steel is subject to a spheroidization heat treatment prior to the deep drawing process, the strength of steel is excessively enhanced by the V precipitation strengthening, which makes it difficult to directly use the steel in the deep drawing process.
In addition, the spheroidization heat treatment may be performed prior to the deep drawing process in order to give suitable workability to the steel. Here, when conventional steels are subject to the spheroidization heat treatment, the spheroidization heat treatment is carried out for a long time (i.e. at least 90 minutes). Therefore, the spheroidization heat treatment has problems in terms of its low steel productivity and high manufacturing cost, and the strength of steel may also be deteriorated due to the decarburization caused by the long-time spheroidization heat treatment.